Traversal is a set of hierarchical intersection tests between a ray and nodes in a bounding volume hierarchy (BVH), until a ray-primitive intersection is found at the leaf nodes. The algorithm often searches for the nearest of such intersections. In an ideal setting, the memory bandwidth of a query directly depends on the number of BV nodes accessed. Thus a high-quality BVH would yield a low bandwidth.
On practical hardware, however, accesses pass through a hierarchy of caches, where a single memory transaction reads multiple BV nodes on the same cache block. This implies that the topology of the BVH and also its mapping to memory addresses (layout) influence the traversal bandwidth.
Depth-first layout (DFL) is the most commonly used node ordering for ray tracing because of its simplicity, and it avoids the storage of one child pointer, since the left child always follows the parent.